A. Technical Field
The present invention relates to a magnetic stripe reader, and more particularly, to systems, devices and methods of directly extracting binary information embedded in a magnetic stripe using simple analog and digital signal processing techniques. This magnetic stripe reader spares a need for a multi-bit analog-to-digital converter (ADC) and a large memory, and thus, constitutes a simple and self-contained solution that reads out the binary information on the magnetic stripe with reduced power consumption and improved cost efficiency.
B. Background of the Invention
A magnetic stripe is widely applied to carry secure information related to financial transactions or personal identity. Secure information is coded into magnetic tracks on the magnetic stripes according to an international standard or a custom protocol compliant with a specific application and industry. A typical magnetic stripe contains three parallel tracks that have a recording density of 75 bits per inch or 210 bits per inch. To date, the magnetic stripe has been embedded in driver's licenses, credit and debit cards, gift or cash cards, loyalty cards, telephone cards, hotel keycards, membership cards, food stamps and many other cards for use in various applications.
Secure information is extracted from the magnetic stripe by physically contacting with or swiping past a magnetic reading head included in a magnetic card reading system. FIG. 1 illustrates a block diagram 100 for a conventional magnetic card reading system, and FIG. 2 illustrates time diagrams 202-204 for relevant signals that are recovered and processed by the conventional magnetic card reading system 100. A magnetic stripe 102 stores multiple bits of data in a band of magnetic material. When the magnetic stripe 102 is swiped through a magnetic reader head (MRH) 104, the MRH 104 detects variation of the magnetic field associated with the magnetic stripe 102. The MRH 104 is commonly made of a coil that is characterized by its parasitic inductance, capacitance and resistance. In the prior art, the MRH 104 is normally coupled with discrete passive components, such that an electrical signal 202 may be properly induced by the MRH 104 in response to the magnetic field. The electrical signal 202 is referred to as a bi-phasic or two frequency (F/2F) data signal, i.e., a F-2F waveform 202, since it alternates between positive and negative flux peaks that are temporally spaced at two characteristic periods, T and T/2. Two sequential T/2 periods 208 are associated with a data bit of “1” while one T period is associated with a data bit of “0”.
The electrical signal 202 is amplified in an amplifier 106, and further sampled and converted to a multi-bit digital signal in an analog-to-digital converter (ADC) 108. The multi-bit digital signal tracks the magnitude of an amplified F-2F waveform according to a sampling frequency. This multi-bit digital signal may be stored in a memory 110 temporarily, and ultimately recovered by a software or hardware decoding block 112 to a digital output 206. The digital output 206 forms a binary bit stream of data that is consistent with the multiple bits of data stored within the magnetic stripe 102.
Both amplitude and frequency of the F-2F waveform 202 may vary by orders of magnitudes. Existing magnetic card reader solutions tackle this challenge by using a large number of external components, using more power or overdesigning. One can loosely divide existing solutions into either analog or digital. In the so-called analog solutions, an overwhelming majority of the read F-2F waveform is processed and decoded continuously using analog functions. This requires additional quiet power supplies, additional pins and a fairly large amount of external components, resulting in a bulky, expensive and power-hungry magnetic card reader system.
On the other hand, digital solutions rely on digital signal processing (DSP) techniques to process and decode the F-2F waveform, and do not require many external components. FIG. 1 illustrates an example of such a digital solution. However, a multi-bit ADC is required to digitize the analog waveform, and a large memory device is needed to store the digitized waveform. To accommodate the large amplitude variations, high-resolution ADCs are applied, and the resolution is higher than what is actually needed for most situations. One extra bit in an ADC increases the area, doubles data to be processed and stored, and quadruples the power consumed by the ADC 108. The digital solutions are inefficient from both perspectives of signal processing and power consumption.
Therefore, despite acceptable performance, most conventional magnetic card readers are plagued by many problems including high cost, large hardware footprint, and large power consumption. A better solution is needed to address the main issues, including cost, hardware footprint and power, with existing magnetic card reader solutions, and particularly, for those low-power applications powered by batteries.